This invention relates to a liquid crystal projector which includes an optical prism unit in which a liquid crystal panel which modulates light in response to a video signal is used.
A liquid crystal projector is known which uses a liquid crystal panel which modulates light in response to a video signal in order to obtain a project image screen of a large size. A conventional liquid crystal projector includes, as principal components thereof, a light source lamp unit, an irradiation optical unit for spectrally separating white light from the light source into light components of red, blue and green and condensing the spectrally separated color light components, an optical prism unit including liquid crystal panels for modulating the condensed light components in response to image information and a dichroic prism for color synthesizing the modulated light components, a projection optical unit for projecting the color synthesized light in an enlarged scale, and a circuit unit including a power supply circuit, a signal processing circuit and so forth.
In recent years, in a liquid crystal projector, a high resolution liquid crystal panel is used in order to project image information as a more distinct picture, and increase in brightness is promoted in order to make the projection screen brighter. A liquid crystal projector of the type described incorporates cooling apparatus for individually cooling the light source lamp unit, circuit unit and liquid crystal panel unit which act as internal heat generating sources. Usually, the cooling apparatus include a cooling fan disposed therein suitably for their application in such a manner as to suck air outside a cabinet into the inside of the cabinet and blast the air to the pertaining unit or units.
FIGS. 5A and 5B show a general configuration of a conventional optical prism unit, and wherein FIG. 5A is a plan view and FIG. 5B is a sectional view taken along line Bxe2x80x94B of FIG. 5A.
Referring to FIGS. 5A and 5B, the optical prism unit 50 shown includes an upper plate 51 and a lower plate 52, a dichroic prism 53 held between the upper plate 51 and the lower plate 52, and three liquid crystal panel units 54, 55 and 56 secured to three different faces of the dichroic prism 53 into which light is introduced. A cooling fan 57 for cooling the optical prism unit 50 is disposed below the lower plate 52. The upper plate 51 and the lower plate 52 are rectangular parallelepipeds and are held in contact with the top and bottom faces of the dichroic prism 53 to held the dichroic prism 53 therebetween.
Air holes 59 for introducing air current from the cooling fan 57 therethrough are formed in a base 58 for the lower plate 52. The air holes 59 are disposed below the liquid crystal panel units 54, 55 and 56 so that air may be brought into direct contact with the liquid crystal panel units 54, 55 and 56. Thus, blast air from the cooling fan 57 passes through the air holes 59 and is brought into direct contact with the liquid crystal panel units 54, 55 and 56 to cool the liquid crystal panel units 54, 55 and 56. The bottom face of the lower plate 52 contacts over the entire area thereof with the base 58 having the configuration just described so that the dichroic prism 53 and so forth are held stably on the base 58.
In recent years, it is demanded to reduce the size of a liquid crystal projector so that it can be carried conveniently. However, since reduction of the size decreases a heat radiating space, the cooling efficiency is deteriorated. Further, as the brightness is increased, the liquid crystal panel generates an increased amount of heat. Therefore, it is a subject to cool the liquid crystal panel units and other units to temperatures lower than their heat-resistant temperatures. In other words, it is a subject to raise the cooling efficiency together with increase of the brightness and reduction of the size.
In the optical prism unit 50 shown in FIGS. 5A and 5B, since the size of the air holes 59 is restricted by the arrangement of the lower plate 52 and the optical units including condensing lenses and mirrors, it is difficult to increase the cooling air amount to the liquid crystal panel units 54, 55 and 56 without increasing the size of the optical prism unit 50. In other words, with the conventional structure, it is difficult to increase the cooling air amount and lower the temperatures in operation of the liquid crystal panels and so forth while reduction of the size is achieved.
It is an object of the present invention to provide a liquid crystal projector which can blast an increased amount of cooling air to raise the cooling efficiency without increasing the size of an optical prism unit.
In order to attain the object described above, according to an aspect of the present invention, there is provided a liquid crystal projector including a dichroic prism, a base for securing the dichroic prism with a plate interposed therebetween, a liquid crystal panel unit disposed on a side face of the dichroic prism, and a cooling fan disposed below the base, the base having an air hole formed therein such that air current generated by the cooling fan is introduced to the liquid crystal panel unit through the air hole to cool the liquid crystal panel unit, a portion of the plate which opposes to the air hole of the base being formed so as to have an inclined face, a curved face or a cutaway portion.
With the liquid crystal projector, the sectional area of the flow path for the air current generated by the cooling fan can be increased by the inclined face, curved face or cutaway portion formed on the plate. Consequently, an increased amount of cooling air can be introduced to the liquid crystal panel unit to cool the liquid crystal panel unit efficiently. More particularly, since the portion of the plate which opposes to the air hole of the base is formed so as to have an inclined face, a curved face or a cutaway portion, it can introduce an increased amount of cooling air to the liquid crystal panel unit to cool the liquid crystal panel unit efficiently. Consequently, the amount of cooling air can be increased to raise the cooling efficiency to lower the temperature in operation of the liquid crystal panel unit without increasing the speed of rotation or the size of the cooling fan. Further, where the cooling efficiency is raised, the speed of rotation or the size of the cooling fan can be reduced, and therefore, a cooling fan of a reduced size can be used to augment the quietness of the liquid crystal projector. Further, since the temperature in operation of the liquid crystal panel unit can be kept low, the life and the reliability of the liquid crystal panel unit are augmented.
According to another aspect of the present invention, there is provided a liquid crystal projector including a dichroic prism, a base for securing the dichroic prism with a plate interposed therebetween, a plurality of liquid crystal panel units disposed on side faces of the dichroic prism, a cooling fan disposed below the base, the base having air holes formed therein such that air current generated by the cooling fan is introduced to the liquid crystal panel units through the air holes to cool the liquid crystal panel units, and air current guiding means provided between the cooling fan and the base for introducing the air current to a particular one of the side faces of the dichroic prism on which a particular one of the liquid crystal panel units is disposed.
With the liquid crystal projector, since the air current guiding means is provided between the cooling fan and the base for introducing the air current to the particular side face of the dichroic prism on which the particular liquid crystal panel unit is disposed, air current generated by the cooling fan can be introduced in a concentrated manner to the particular liquid crystal panel unit which exhibits a comparatively high temperature in operation. Consequently, the temperatures in operation of the liquid crystal panel units can be made uniform among them. Therefore, there is no necessity any more to raise the speed of rotation or increase the size of the cooling fan in accordance with that one of the liquid crystal panel units which exhibits a comparatively high temperature in operation.
Where the liquid crystal panel units are liquid crystal panel units for red, green and blue, preferably the liquid crystal panel unit for blue is disposed on the particular side face of the dichroic prism. Since the liquid crystal panel unit for blue exhibits a higher temperature in operation than the other liquid crystal panel units for red and green, it is desirable to cool the liquid crystal panel unit for blue in a concentrated manner. In other words, the different temperatures in operation (blue greater than green greater than red) of the liquid crystal panel units for red, green and blue which are caused by a difference in wavelength of transmission light through them can be uniformed. Therefore, there is no necessity any more to raise the speed of rotation or increase the size of the cooling fan in accordance with the liquid crystal panel unit for blue which exhibits the highest temperature in operation.
Preferably, the air current guiding means is an inclined face provided on the plate. The air current generated by the cooling fan can be introduced to the particular face of the dichroic prism efficiently along the inclined face provided on the plate. In particular, the air current generated by the cooling fan and introduced in through the air holes of the base is introduced to the particular liquid crystal panel unit by the inclined face formed on the plate and cools the particular liquid crystal panel unit efficiently. Consequently, the temperature in operation of the particular liquid crystal panel unit on the particular face of the dichroic prism can be lowered without increasing the size of the plate.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.